A missing tag that is expected in a combination such as a name on a street, tracktype on a track, etc. I forgot to check name/tracktype/x can someone go there and check that ?

Other mappers already know the tag x is missing because there is no tag x! If you desperately want to fix tag x, go back there! Spamming the fixmes with "please improve this place" will probably reach the opposite goal where mappers are going to get the alert tools spammed!

Automated data checks and error detections are useful, but are better presented as an overlay in a separate tool. We already have many Quality Assurance tools which do this, and many which handle a range of different classes of error. For example a new type of error can be added to Osmose or JOSM/Validator or perhaps set up as a new challenge in MapRoulette.

OsmAnd has a "OSM Mapper assistant" option that (among other things) draws fixme tags. It can be found under "Configure Map" -> "Details". This works with the default style, but not necessarily other map styles.